1. Field of the Invention
The present invention relates to a rotation detecting device for detecting rotation of a vehicle engine, wheel rotation speed or the like and, particularly, a rotation detecting device that employs magnetoresistance elements or hall elements.
2. Description of the Related Art
U.S. Pat. No. 6,366,079 B1 or JP-A-2001-153683, which is a publication of its counterpart Japanese patent application, discloses a common rotation detecting device. Such a rotation detecting device provides rotation data of an engine crankshaft by detecting changes in a magnetic field caused by rotation of a rotary magnetic member that is rotated by the engine crankshaft. As shown in FIG. 6, such a rotation detecting device includes a bridge circuit 3 of four magnetoresistance sensors MRE 1, MRE 2, MRE 3, MRE 4 and a signal processing circuit, which are formed in an IC chip. The IC chip is disposed on a surface of a member formed at a distance L from the rotary magnetic member. The signal processing circuit includes a differential amplifier 4 and a comparator 5 The IC chip is covered with a coating member of resinous material, from which electric terminals including a power terminal to be applied a voltage (+V), an output terminal T2 and a ground terminal are drawn out. In that common rotation detecting device, a variation in the distance between the magnetoresistance sensors and the rotor member causes one of major errors in the rotation data.
U.S. Pat. No. 6,812,694 B2 or its counterpart Japanese patent application JP-A-2004-301645 discloses another common rotation detecting device. In this rotation detecting device, a similar problem is caused by a variation in the distance between the magnetoresistance sensors and the rotor member.